It is frequently desirable, for such purposes as target practice, decoys, missile system development, and scientific data, to provide small, low-cost, gas-generating devices which can simulate effectively the plumes of turbojet engines in terms of such characteristics as size and radiant emission, particularly in the infrared wave lengths. It is well known that turbojet engines are primarily liquid-fueled, are employed as the propulsion means for endoatmosphere aircraft, and produce infrared radiant plumes of different size and intensity depending on the particular engine and aircraft.
For the purposes aforedescribed, the simulating device must be relatively small, low cost, and preferably readily expendable. Plume-generating drones have hitherto been employed, but it has been found that their plumes have inadequate radiation characteristics and are frequently too small to be effective simulators of turbojet plumes. Small, solid-propellant rockets which have been developed for such purposes as missiles or meteorological and other upper atmosphere scientific data gathering devices, cannot be employed for the present purpose since they are designed for maximum thrust power or specific impulse and therefore do not produce plumes of the kind desired. Exhaust velocity of the solid particles is too high to give the desired infrared signatures. For example, loading such rockets with fuel-rich propellants essentially burdens them with inert components which reduce specific impulse unless the rocket is equipped with an upstream after-burner device where oxidation is completed, as, for example, with the use of ram air, prior to venting of the combustion products of the rocket into atmosphere. Additionally, exhaust velocity of any solid particles produced is too high to provide the desired infrared signatures.
The term "fuel rich" as employed herein means a gas-generating composition which contains an insufficient number of oxygen atoms available to convert both carbon to carbon monoxide and the inorganic particulates to the stable inorganic oxide. In the event that the inorganic component is non-oxidizable, the number of available oxygen atoms present are insufficient to oxidize the carbon to CO. In making the stoichiometric calculations required to ensure fuel-rich formulations, no provision is made for the oxidation of hydrogen atoms which may be present.
It has been found that particulate solids within a size range of about 0.01 to 100 microns produce much higher radiant intensities than equal masses of either gases or particulate smaller or larger solids. Within the given size range, the radiation characteristics of the particles may be tailored to a wide range of requirements primarily by varying the size and material of the particles.
Although some of the fuel-rich gas-generating compositions employed in the process of the invention have been generically described in the prior art for such purposes as air-augmented high-performance rockets, or as gas-generating propellants, none of the art to applicant's knowledge discloses a process for simulating the plume, in size and radiant intensity, of a turbojet engine or the specific conditions required in the formulation of the gas-generating compositions employed in the process to produce a plume having the required radiation and size characteristics either per se or in combination with a plume which is inadequate in these respects.